كيميا همتي

Traditional cellular systems face challenges such as inter-cell interference an‎d performance degradation at the cell edges. Cell-Free Massive Multiple-Input Multiple-Output (CF-mMIMO) systems have been proposed as a key technology for future generations to enhance communication capacity an‎d quality. However, increasing capacity in these systems requires the deployment of a large number of Access Points (APs), which leads to increased cost, power consumption, an‎d computational complexity. In this regard, this thesis investigates a combination of three emerging technologies. This combination includes the utilization of Reconfigurable Intelligent Surfaces (RIS) to improve capacity with low cost an‎d power consumption, the adoption of the Terahertz (THz) ban‎d due to its wide ban‎dwidth, an‎d the implementation of user-centric clustering to reduce computational load an‎d enhance scalability. The use of RIS in the Terahertz ban‎d helps to create virtual Line-of-Sight (VLoS) paths, while user-centric clustering manages the interference an‎d computational burden resulting from the dense deployment of APs. The objective of this thesis is to design decentralized beamforming for the downlink of a user-centric, RIS-assisted cell-free network operating in the Terahertz ban‎d. This design is formulated as a non-convex optimization problem aiming at the joint optimization of the precoding matrix at the APs, the phase-shift matrix at the RIS, an‎d the combining vector at the receiver, in order to minimize the weighted sum Mean Square Error (WMMSE) of the users. Simulation results show that the proposed clustering algorithm, while significantly reducing computational complexity an‎d increasing scalability, introduces only a minor dro‎p (around 15%) in sum-rate performance compared to the full cooperation (non-clustered) scenario. These results confirm the efficiency, scalability, an‎d practical implementability of the proposed system in future-generation networks.

سيستم‌هاي انبوه آنتني بدون سلول , سطوح بازتابي هوشمند , باند تراهرتز , خوشه‌بندي كاربر‌محور

Cell-free massive multiple-input multiple-output (CF-mMIMO) , intelligent reflecting surfaces (IRS) , user-centric clustering , terahertz (THz) band

Kimia Hemati

Dr. S.Mohammad Razavizadeh